Field
This application relates generally to sensor systems, and more particularly to optical-fiber-compatible acoustic sensor systems.
Description of the Related Art
In membrane-based fiber acoustic sensors, a deflectable membrane is used as a transducer to convert the small vibration induced by an incident acoustic wave into an optical modulation. See, e.g., M. J. Gander, W. N. MacPherson, J. S. Barton, R. L. Reuben, J. D. C. Jones, R. Stevens, K. S. Chana, S. J. Anderson, and T. V. Jones, “Embedded micromachined fiber-optic Fabry-Perot pressure sensors in aerodynamics applications,” IEEE Sens. J. 3, 102-107 (2003); L. H. Chen, C. C. Chan, W. Yuan, S. K. Goh, and J. Sun, “High performance chitosan diaphragm-based fiber-optic acoustic sensor,” Sensors Actuators A Phys. 163, 42-47 (2010); J. A. Bucaro, N. Lagakos, and B. H. Houston, “Miniature, high performance, low-cost fiber optic microphone,” J. Acoust. Soc. Am. 118, 1406-1413 (2005); F. Xu, J. Shi, K. Gong, H. Li, R. Hui, and B. Yu, “Fiber-optic acoustic pressure sensor based on large-area nanolayer silver diaphragm,” Opt. Lett. 39, 2838-40 (2014); S. E. U. Lima, O. Frazão, R. G. Farias, F. M. Araújo, L. A. Ferreira, V. Miranda, and J. L. Santos, “Intrinsic and extrinsic fiber Fabry-Perot sensors for acoustic detection in liquids,” Microw. Opt. Technol. Lett. 52, 1129-1134 (2010).
These devices are interesting because they are compact, they can exhibit a high sensitivity and a low noise, and they are easily optically multiplexed into large arrays. The high sensitivity arises in part from the high compliance of sub-micron diaphragms, which will deflect by measurable amounts even under a very slight pressure (e.g., about 90 nm/Pa for a 450-nm thick square diaphragm, 370 μm on the side; see, e.g., W. Jo, O. C. Akkaya, O. Solgaard, and M. J. F. Digonnet, “Miniature fiber acoustic sensors using a photonic-crystal membrane,” Opt. Fiber Technol. 19, 785-792 (2013)). Because of this unique set of features, such devices are being studied and developed for a large number of important applications ranging from seismic research (see, e.g., G. Gagliardi, M. Salza, P. Ferraro, P. De Natale, A. Di Maio, S. Carlino, G. De Natale, and E. Boschi, “Design and test of a laser-based optical-fiber Bragg-grating accelerometer for seismic applications,” Meas. Sci. Technol. 19, 085306 (2008)) to large structure monitoring (see, e.g., M. Majumder, T. K. Gangopadhyay, A. K. Chakraborty, K. Dasgupta, and D. K. Bhattacharya, “Fibre Bragg gratings in structural health monitoring—Present status and applications,” Sensors Actuators A Phys. 147, 150-164 (2008)), underwater surveillance (see, e.g., D. Hill and P. Nash, “Fiber-optic hydrophone array for acoustic surveillance in the littoral,” in Photonics for Port and Harbor Security, M. J. DeWeert and T. T. Saito, eds., International Society for Optics and Photonics, 2005, pp. 1-10), MRI-compatible microphones (see, e.g., M. S. NessAiver, M. Stone, V. Parthasarathy, Y. Kahana, A. Paritsky, and A. Paritsky, “Recording high quality speech during tagged cine-MRI studies using a fiber optic microphone,” J. Magn. Reson. Imaging 23, 92-7 (2006)), photoacoustic imaging (see, e.g., P. C. Beard, F. Pérennès, E. Draguioti, and T. N. Mills, “Optical fiber photoacoustic—photothermal probe,” Opt. Lett. 23, 1235 (1998)), small force measurements (see, e.g., W. Jo and M. J. F. Digonnet, “Piconewton force measurement using a nanometric photonic crystal diaphragm,” Opt. Lett. 39, 4533 (2014)), atomic force microscopy (see, e.g., D. Rugar, H. J. Mamin, and P. Guethner, “Improved fiber-optic interferometer for atomic force microscopy,” Appl. Phys. Lett. 55, 2588 (1989)), and bio/chemical sensors (see, e.g., X.-D. Wang and O. S. Wolfbeis, “Fiber-optic chemical sensors and biosensors (2008-2012),” Anal. Chem. 85, 487-508 (2013)). Most of these applications utilize very low minimum detectable pressures (MDPs). For example, for underwater oil and gas exploration, the detected pressure is typically in the range of 10-200 μPa/√Hz over a frequency that spans from 100 Hz to 20 kHz.